It is proposed to study factors involved in the control of antibody affinity, that is those factors controlling the selection of B-lymphocytes to proliferate and secrete antibody. Towards this goal experiments will be carried out to detemine (1) the effect of epitope density on the ability of an antigen to stimulate low affinity antibody synthesis, (2) the effect of T-lymphocyte tolerance on antibody affinity, (3) the T-cell dependence of high affinity as compared with low affinity antibody synthesis and (4) the role of genetic factors in influencing the ability of animals to form high affinity antibody. It has been shown that the ability to form high affinity antibody is under some type of genetic control. Experiments are planned to analyze the nature of the genetic influence on antibody affinity.